Apparatus, system and methods for measuring a blood pressure gradient

ABSTRACT

An apparatus, control system and methods are disclosed for directly measuring a blood pressure gradient, i.e. by real-time pressure measurements, with particular application for in situ measurement of transvalvular blood pressure gradients for the aortic valve and other heart valves, using minimally-invasive techniques. The apparatus takes the form of a multi-sensor assembly, enclosed within a micro-catheter or a steerable guidewire, and comprises a plurality of optical pressure sensors arranged along a length of the distal end portion, for measuring pressure simultaneously at each sensor location. For example, four MOMS optical pressure sensors, and optionally, a temperature and/or flow sensor, are incorporated into a distal end portion having a diameter of 0.89 mm or less, and preferably 0.46 mm or less. Beneficially, all sensors are optically coupled, via respective optical fibers, to an optical coupler at the proximal end of the multi-sensor apparatus, without requiring electrical connections.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/354,624, which is a national stage entry of PCT International patentapplication no. PCT/IB2012/055893, having an international filing dateof Oct. 26, 2012, which claims priority from U.S. provisional patentapplication No. 61/552,778 entitled “Apparatus, system and methods formeasuring a blood pressure gradient”, filed Oct. 28, 2011 and from U.S.provisional patent application No. 61/552,787 entitled “Fluidtemperature and flow sensor apparatus and system for cardiovascular andother medical applications”, filed Oct. 28, 2011, all of which areincorporated herein by reference, in their entirety.

TECHNICAL FIELD

This invention relates to an apparatus, system and methods for measuringfluid pressure gradients, and in particular, relates to measurement ofblood pressure gradients and flow within the heart or blood vessels,including measurement of transvalvular blood pressure gradients.

BACKGROUND ART

In vertebrate animals, the heart is a hollow, muscular organ having fourpumping chambers: the left and right atria and the left and rightventricles, each being provided with its own one-way valve. Thus, thereare four heart valves: the mitral valve and the tricuspid valve, whichare called atrio-ventricular valves, and the pulmonary valve and theaortic valve, which are called ventriculo-arterial valves. In one cycleof cardiac contraction, a valve opens to let blood flow from one side tothe other, and then it closes to prevent backflow in the otherdirection. Thus, in the diastolic phase, the atrio-ventricular valvesopen to enable filling of the ventricles while the ventriculo-arterialvalves remain closed. Conversely, in the systolic phase (ventricularcontraction) of the cardiac cycle, the mitral and tricuspid valvesclose, while the pulmonary and aortic valves open to enable ejection ofblood downstream of the ventricles.

Heart valve disease or dysfunction can, in severe cases, substantiallyrestrict day to day activities and shorten the lives of patients. Theprimary procedure is valve repair or replacement surgery. In more than20 percent of cardiac surgeries, heart valve disease represents theprincipal reason for a type of cardiac operation known as “open heart”surgery. These operations are associated with significant morbidity andmortality according to multiple risk factors related to age. Newminimally-invasive procedures have been proposed to improve overallsuccess. They involve inserting a valve made from animal tissue into thebody using catheters and placing it inside the original diseased valve.However, both valve repair and replacement techniques remainparticularly expensive and are associated with important risks for thepatients.

It is therefore important to be able to quantify accurately the severityof valve disease, identify the right diagnosis and provide the propertreatments to patients. In addition, following a heart valve procedure,it is also fundamental to assess and monitor the physiologic performanceof the new or repaired valve.

Heart valve pathologies may include a defect in closing or opening of avalve, or a combination of these two dysfunctions. Epidemiologically, adefect in opening of the aortic valve remains one of the most frequentanomalies. The three usual causes of aortic valve stenosis remain, inorder of importance: calcified degeneration of the valve attributable toage, but certainly accentuated by hypertension; a congenital anomalycalled bicuspid aortic valve, in which the valve possesses only tworather than three cusps (a cusp may also be referred to as a leaf orleaflet); and acute rheumatic fever (a particular bacterial infection atan early age, with subsequent excess scarring).

Diagnosis of aortic valve stenosis relies, first and foremost, on theappearance of symptoms in the patient, namely, breathlessness and chestpain on exertion, as well as loss of consciousness. Diagnosis is madethrough physical examination of the patient revealing a characteristicsystolic murmur on auscultation, and a slower than normal rise of thepulse. Following that, transthoracic echography may confirm the clinicalimpression, e.g. by measuring an abnormal thickening of the layers ofthe heart valves, presence of calcifications, as well as restriction ofthe movement of the opening of the valve (Braunwald's Heart Disease: ATextbook of Cardiovascular Medicine, Authors: Peter Libby, Robert O.Bonow, Douglas L. Mann and Douglas P. Zipes, pages 267-268). The Dopplereffect can be used to measure the velocity of blood traversing throughthe valve. This type of examination (two dimensional imaging andDoppler) allows for evaluation of the maximal velocity of thetransvalvular blood flow, the aortic valve surface area and the surfacearea of the left ventricle outflow tract (LVOT). Accordingly, a severeaortic stenosis is defined by:

a) maximal flow velocity of >4.5 m/sec;

b) a mean transvalvular pressure gradient>50 mmHg;

c) a ratio of the surface of the LVOT/aortic valve×TVI (Time VelocityInterval)<0.25;

or

d) an estimated valve surface area of <0.75 cm² (Braunwald's HeartDisease: A Textbook of Cardiovascular Medicine, Authors: Peter Libby,Robert O. Bonow, Douglas L. Mann and Douglas P. Zipes, page 269).

Even though echo-cardiography remains the most frequently used methodfor confirmation of diagnosis, it is limited by the echogenicity of thepatient, valvular calcifications and sub-valvular calcifications, aswell as the presence of concomitant mitral valve pathology. The resultsof echo-cardiography are also strongly operator-dependent. Consequently,it would be preferable to have a diagnostic method that relies on an insitu measurement of the transvalvular pressure gradient, made directlyvia cardiac catheterization into the interior of the heart in the regionof the valve concerned, and surrounding regions.

In situ measurements of pressure or flow can be made within the humanbody, by minimally-invasive techniques, using a pressure sensingcatheter or a special guidewire equipped with an integrated pressuresensor (see, for example, Grossman's cardiac catheterization,angiography, and intervention, Authors: Donald S. Baim and WilliamGrossman, pages 647-653).

Classically, this measurement of a transvalvular pressure difference, orpressure gradient, is made by two pressure sensing catheters positionedupstream and downstream, respectively, of the valve of interest, e.g.the aortic valve. To do this, the transeptal approach uses aBrockenbrough needle, and a Mullins type catheter to permit access, viathe femoral vein, to the left atrium, by perforating the inter-atrialseptum, then traversing the mitral valve, to place the tip of thecatheter in the left ventricular cavity. A second catheter is introducedthrough the common femoral artery, to be positioned in the ascendingaorta, just above the cusps of the aortic valve. Simultaneousmeasurements of the pressure upstream and downstream of the aortic valvecan thus be obtained.

An alternative to this method involves placing a first arterial catheterthrough the aortic valve in the left ventricle and then introducing asecond arterial catheter, and positioning it above the aortic valve inthe ascending aorta. However, in this technique there is an exaggerationof the transvalvular pressure gradient since one of the catheters reststhrough the valve.

In another method, one can also simply measure the transvalvulargradient with only one arterial catheter, by a “pull back” method, i.e.inserting the catheter, crossing the valve into the ventricle and oncethe ventricular pressure measurement has been made, quickly withdrawingfrom the left ventricle into the ascending aorta, and subsequentlymeasuring the aortic pressure. This last technique is clearly lessreliable since, firstly, the measurements of the aortic and ventricularpressures are not simultaneous and secondly, the withdrawal of thecatheter frequently involves a benign transitory cardiac arrhythmia,which distorts the pressure curves.

A variant of the latter approach was reported in an experimental study(Feasibility of a Pressure Wire and Single Arterial Puncture forAssessing Aortic Valve Area in Patients with Aortic Stenosis, J. H. Baeet al., J. Invasive Cardiol., 2006 August, 18(8), pp. 359-62). Apressure sensing wire, inserted through a guiding catheter, was used tomeasure pressure in the left ventricle using the pressure sensing wire,while simultaneously measuring pressure in the aorta using the guidingcatheter. In practice, the technique is used infrequently. Firstly, itis not ideal to use different types of devices for comparing the twopressures. Also, in practice, the pressure sensing wire described isused for measuring pressures within small blood vessels, such ascoronary arteries, and is therefore of small diameter and very flexible.It is therefore too limp and fragile for reliably positioning it forpressure measurements within the heart, where higher blood flows andsignificant turbulence in the flow tends to cause movement of the sensorat the end of the wire.

To calculate the cardiac flow, thermodilution by a Swan-Ganz catheter orthe method of Fick are commonly used (Grossman's cardiaccatheterization, angiography, and intervention, Authors: Donald S. Baimand William Grossman, pages 150-156).

Besides diagnosing a heart valve condition, measurements of a bloodpressure gradient in blood vessels may be used to diagnose and treatpatients with multi-site vessel disease. In order to quantify lesionseverity in a diffusely affected vessel, pressure measurements are madeat several locations along the vessel. This is currently done bywithdrawing a pressure sensor equipped guidewire along a length of thevessel from a distal to a proximal position very slowly during asteady-state maximum induced hyperaemia. This diagnostic shows thelocation and severity of lesions but accuracy is compromised by thesequential nature of the data.

In view of limitations, such as limited accuracy, of the above-mentionedapparatus and techniques, there is a need for improved or alternativesystems, apparatus and methods of operation for directly measuring andmonitoring blood pressure gradient in real time, more accurately andreliably than is now possible, using minimally-invasive techniques.

A pressure sensing catheter is effectively a fluid-filled catheter: apressure at the distal end, positioned in the region of interest, ismeasured by monitoring the fluid pressure in the catheter at theproximal end. A pressure sensing catheter for sensing pressure withinthe heart is typically 6 to 8 French in outer diameter (0.078″ to0.104″), in order to maintain enough rigidity and robustness. Typically,a pressure sensing guidewire equipped with an electrical pressure sensorcan be made with a smaller diameter. This is advantageous forapplications such as transvalvular pressure measurements or formeasurements in small blood vessels such as coronary vessels.

One type of commercially available sensor equipped guidewire,PressureWire Certus from St. Jude Medical, uses aMicro-Electro-Mechanical-Systems (MEMS) device that includes apiezoresistor and diaphragm, e.g. as described in U.S. Pat. Nos.5,343,514 and 6,615,667 to Smith (Radi Medical Systems AB) entitled“Combined flow, pressure and temperature sensor”. Deformation of thediaphragm, caused by a pressure change, is read using resistance values.Other similar systems using MEMS technologies monitor the capacitancevalue between a fixed plate and the diaphragm to evaluate thedeformation of the diaphragm due to pressure changes.

As explained above, available single pressure sensor guidewires canmeasure pressure at only one point at a time, and to measure a pressuregradient, the guidewire sensor must be moved through a region ofinterest, such as through a heart valve, or other vascular region, tomeasure pressure sequentially at several different points.

A problem with guidewires equipped with sensors based on electricalsignals is that multiple, long electrical connections to each sensormust be provided. The length of a guidewire may be more than 1 meter.Use of microelectronics and long electrical wires, particularly whenused in humid biological conditions, tends to cause reliability issueswith measurement of small electrical signals, e.g. from parasiticcapacitances, noise and electromagnetic interference (EMI), and limitsthe ability to integrate multiple electrical sensors within a guidewireto measure pressure gradient and flow. Furthermore, there may besignificant risks involved with the use of microelectronics andelectrical connections in vivo, particularly in the region of the heart,where electrical activity may disrupt normal heart function.

The electronic drift of MEMS sensors integrated into guidewires remainsa limitation. For example, in one study, it was reported that measuredpressures dropped >5 mmHg/hour, due to drift, therefore causing pressuregradient over-estimation (Coronary Pressure, Authors: Nico Pijls andBernard de Bruyne, pages 125-127).

Additionally, the guidewire is fabricated to provide the requiredflexibility and torque characteristics to enable the guidewire to besteered and positioned. Thus, the guidewire usually includes torquesteering components comprising a central core-wire or mandrel, andexternal coil, e.g. a fine spiral metal coil, and a J-shaped tip(pre-shaped or manually shaped).

A guidewire used for cardiology may typically have a gauge of between0.89 mm (0.035″) and 0.25 mm (0.010″) for introduction into small bloodvessels. Note: catheter gauge may also be specified in French units: 1French=0.333 mm diameter (0.013″). It will be appreciated that there isa limit to the number of electrical wires, sensors and steeringcomponents that can physically fit within the required diameterguidewire. Even if larger guidewires could be inserted, they would tendto interfere with normal operation of a heart valve and distortmeasurements, so it is desirable that the guidewire is as small gauge aspossible. This presents a number of challenges in providing a guidewirewith more than one electrical sensor.

In addition, MEMS sensors along with their long electrical connectionssignificantly increase the complexity of manufacturing assemblyprocesses of guidewires using electrical sensors, and thereforesignificantly increasing their manufacturing costs. Typically,guidewires for medical use are fabricated to be disposable (i.e. forsingle use only) and are significantly expensive.

To provide multi-sensor capability with a single electrical connection,U.S. Pat. No. 6,615,667 discloses a single combined flow, pressure andtemperature MEMS sensor, but again, pressure can be measured at only onepoint.

To avoid the need for wired electrical connections entirely, opticalpressure sensors are also known which are optically coupled to thecontrol unit by optical fibers. However, another challenge for medicalapplications, as described above, is that to measure pressure gradients,pressure sensors are required having sufficient sensitivity to detectsmall pressure differences reliably within the region of interest. Someavailable optical sensors are either too large to allow for multiplesensors to be accommodated in a small gauge device, and/or they do nothave sufficient sensitivity.

U.S. Pat. No. 4,735,212 to Cohen (Cordis Corporation) entitled “Multiplesite fiber-optic pressure transducer” and U.S. Pat. No. 4,543,961 toBrown (Cordis Corporation) entitled “Data transmission system” disclosesearly designs for integrating several miniaturized pressure transducersor sensors arranged in a relatively large, i.e. 1.5 mm (0.060″) singlefiber device. These designs are quite complex and would appear to be achallenge to fabricate consistently. More significantly, the sensorelements will be sensitive to stresses when the fiber is bent ortwisted, such that it would be difficult to discriminate fiber stressesfrom actual pressure readings. Thus, even if they could be manufacturedwith sufficiently small diameters, these and similar configurationswould not be suitable for intravascular or intravalvular use whichnecessitate bending of the fiber in the region of the sensors.

Another known type of single point optical pressure sensor is aMicro-Opto-Mechanical Systems (MOMS) device that comprises a Fabry-Perotoptical cavity where one of the two mirrors is a diaphragm.Low-coherence light is sent to the cavity via an optical fiber.Diaphragm motions are measured from spectral changes of the reflectedlight. Miniaturized pressure sensors of this type are described, forexample, in U.S. Pat. No. 6,684,657 to Donlagic et al. (FisoTechnologies Inc.) entitled “Single Piece Fabry-Perot Optical Sensor andMethod of Manufacturing the Same”, and also in U.S. Pat. No. 7,689,071to Belleville et al. (Opsens Inc.) entitled “Fiber-optic pressure sensorfor catheter use”. The use of this type of sensor for use incardiovascular applications is relatively recent.

In summary, existing guidewire apparatus, using various types ofsensors, are available for single point pressure measurements, forexample, from St. Jude Medical and Volcano Corporation. However,apparatus is not currently known or available to cardiologists fordirectly measuring in situ blood pressure gradients simply and quickly,particularly transvalvular pressure gradients, where a catheter with adiameter of 0.89 mm (0.035″) and preferably 0.46 mm (0.018″) or less isneeded to minimize disruption to normal heart valve activity and overestimation of transvalvular gradient. It would also be desirable toenable measurements for simultaneous determination of cardiac output andvalvular area.

Thus, there is a need for improved or alternative systems, apparatus andmethods for direct measurement and monitoring of blood pressure,pressure gradients and/or flow within the heart and the vascular system,and in particular, for measurement of transvalvular pressure gradientsand flow velocity.

SUMMARY OF INVENTION

The present invention seeks to mitigate one or more disadvantages of theknown systems, apparatus and methods, or at least provide analternative.

Aspects of the invention thus provide an apparatus, system and methodsfor measuring a fluid pressure gradient, such as a blood pressuregradient, using a multi-sensor assembly, which may take the form of amicro-catheter or steerable guidewire, for example. Preferably, multipleoptical micro-sensors allow for measuring pressure at multiple locationssimultaneously and optionally, one or more other sensors may be providedfor measuring flow velocity, or other parameters such as temperature.

Thus, a first aspect of the invention provides an apparatus formeasuring a fluid pressure gradient comprising: a multi-sensor assemblyextending from a proximal end to a distal end portion, the distal endportion comprising a sensor means comprising a plurality of opticalsensors for measuring pressure at a plurality of locations along alength of the distal end portion; an optical coupling between each ofthe plurality of optical sensors and an optical input/output at theproximal end; a covering layer extending over the multi-sensor assemblyand providing an aperture adjacent each optical sensor; and the distalend portion thereof having a diameter suitable for introductionintravascularly or intraluminally through a micro-catheter.

The optical sensors preferably comprise Micro-Opto-Mechanical Systems(MOMS) pressure sensors, and more preferably comprise Fabry-Perot MOMSsensors.

The optical sensors are optically coupled to an optical input/output ata proximal end of the micro-catheter or guidewire via optical fibers, orother flexible light guides. The optical coupling preferably comprises aplurality of optical fibers, and each optical pressure sensor isoptically coupled to the input/output by a respective one of theplurality of optical fibers. The sensor means may optionally comprise aflow sensor, which is preferably an optical flow sensor, but may also bean electrical flow sensor or other appropriate type of flow sensor.

When the flow sensor comprises an optical flow sensor, for example, anoptical thermoconvection flow sensor, the optical coupling furthercomprises an optical fiber coupling the optical flow sensor to theoptical input/output. Thus, the apparatus comprises sensor meanscomprising an arrangement of a plurality of optical sensors and aplurality of optical fibers, each fiber coupling at least one opticalpressure sensor or an optical flow sensor to the optical input/output atthe proximal end.

The flow sensor may comprise an electrical flow sensor and themulti-sensor assembly further comprises electrical connections couplingthe electrical flow sensor to an electrical input/output at the proximalend. The flow sensor may comprise a resistive/ohmic thermoconvectionflow sensor, or alternatively a Doppler effect flow sensor.

The covering layer may, for example, comprise polymer tubing in the formof a micro-catheter surrounding the sensor means and the plurality ofoptical fibers, the micro-catheter extending from the proximal end to atip at the distal end, and the micro-catheter having an aperture in thedistal end portion adjacent each sensor.

The covering layer or micro-catheter comprises, for example, a polymertubing, which may be polyimide or PTFE, for example, or other suitableflexible, bio-compatible or hemo-compatible material, with appropriatemechanical properties. In some embodiments, the covering layer comprisesa multilayer tubing. Preferably, the outside diameter of the polymertubing surrounding at least said length of the distal end portion has adiameter of 0.89 mm (0.035″) or less. More preferably, the diameter is0.46 mm (0.018″) or less. Thus, the outer layer, or covering, enclosesand protects the multi-sensor assembly along the length of the opticalfibers and comprises an aperture adjacent each pressure sensor, i.e. toallow contact of surrounding fluid with each sensor for pressuremeasurement. An outer protective jacket may also be provided around theproximal end portion.

Preferably, the dimensions of the components of the multi-sensorassembly provide for an apparatus wherein the distal end portion has anoutside diameter of 0.89 mm (0.035″) or less, and more preferably of0.46 mm (0.018″) or less.

Thus, in one embodiment, suitable for measurement of transvalvularpressure gradients, the apparatus comprises a plurality of sensorsprovided along a length of the distal end portion, for example, four ormore optical pressure sensors arranged at intervals along a length of 4cm to 7 cm of the distal end portion, near the distal tip. The overalllength of the multi-sensor apparatus may be 1 m to 2 m, typically 1.5 mto 1.8 m.

In apparatus for medical applications, it is desirable that themulti-sensor assembly is enclosed within an envelope or outer/coveringlayer that extends along its length. A suitable flexible covering layerprotects the optical components, while allowing the apparatus to beintroduced intraluminally or intravascularly, and/or filled or flushedwith fluid, such as saline solution.

In some embodiments, the apparatus further comprises torque steeringcomponents, e.g. a mandrel, which may alternatively be referred to as acore-wire, extending axially along the length of the multi-sensorassembly and an outer layer comprising a coil, i.e. a fine wire coilsimilar to that of a conventional guidewire. The latter may have anexternal diameter along the length of the distal end portion of <0.89 mmand preferably 0.46 mm or less, and optionally may comprise a J-tip.Thus, the multi-sensor apparatus takes the form of a steerableguidewire, with the coil acting as the covering layer, enclosing thesensors and their optical fiber connections to the input/outputconnector. The coil provides apertures near each sensor to allow forfluid contact during pressure measurements in a surrounding fluid.

The optical input/output means may comprise part of an optical connectorat the proximal end for coupling the multi-sensor apparatus to a controlsystem, i.e. to provide optical coupling for each optical sensor, andoptionally the connector provides an electrical connection for anelectrical sensor, if required. The input/output means may furtherprovide for wireless connectivity with the control system.

In an embodiment of an apparatus for measuring a transvalvular orintra-arterial blood pressure gradient and flow velocity, the sensingmeans comprises a plurality of at least four optical pressure sensorsand an optical flow sensor arranged along a length of the distal endportion matched to a dimensions of the transvalvular or intra-arterialregion of interest; and each sensor is optically coupled to theinput/output means at the proximal end by a respective individualoptical fiber, each of the sensors and optical fibers having outsidediameters such that they are accommodated within a catheter or guidewirehaving an outside diameter of <0.89 mm and preferably 0.46 mm or less.

In another embodiment of an apparatus for measuring a transvalvular orintra-arterial blood pressure gradient and flow velocity, the sensingmeans comprises a plurality of at least four optical pressure sensorsand an electrical flow sensor, arranged along a length of the distal endportion matched to a dimension of the transvalvular or intra-arterialregion of interest; each optical pressure sensor is optically coupled tothe input/output means at the proximal end by a respective individualoptical fiber, and the electrical flow sensor is provided with a pair ofelectrical connections; each of the sensors, the optical fibers and theelectrical connections have outside diameters such that they areaccommodated within a catheter or guidewire having an outside diameterof <0.89 mm and preferably 0.46 mm or less.

Thus, for example, a small gauge multi-sensor apparatus forintravascular use may comprise, e.g., two, four or perhaps eightpressure sensors arranged at the distal end for sensing pressure at aplurality of locations simultaneously, together with a flow sensor formeasuring flow velocity.

In one embodiment, a small gauge multi-sensor wire comprises fouroptical pressure sensors arranged along a length, e.g. 4 cm to 7 cm, atthe distal end of the wire, which allows for placement of two sensors oneach side of a heart valve, to allow direct measurement of thetransvalvular pressure gradient, with minimal disruption to the valvefunction.

In some embodiments, a plurality of optical pressure sensors may becombined with an electrical flow sensor, e.g. a conventional ohmicthermoconvection flow sensor may be used, thus requiring only one pairof electrical wires. Optionally, additional types of sensors, such as atemperature sensor may be included.

The multi-sensor wire may be provided in a micro-catheter and have astraight tip to allow it to pass easily through a heart valve, and sothat it may be introduced through a conventional support catheter orguide catheter, which may already be in place for other cardiacprocedures. Optionally, the multi-sensor wire may comprise torquesteering elements, such as a conventional mandrel and coil arrangement,and optionally, a J-shaped tip, to allow the multi-sensor wire to beintroduced, torqued and steered as a conventional guidewire.

Yet another aspect of the invention provides a control system for amulti-sensor wire apparatus, wherein the control system comprises alight source means and detection means for coupling to each of theoptical sensors. The control system optionally comprises electricalconnections for an electrical sensor.

The system may further comprise processing means, comprising hardwareand/or software, for processing optical data indicative of pressuregradient values and/or optical or electrical data indicative of flowvelocity values, and deriving pressure and flow data therefrom.

In an embodiment, a system for measuring an intravascular ortransvalvular blood pressure gradient further comprises processingmeans, e.g. hardware and/or software, for graphically displaying datarepresenting a blood pressure gradient and/or flow velocity data for oneor more time intervals, and during one or more cardiac cycles.

Another aspect of the invention provides a multi-sensor-assembly for anapparatus for measuring a fluid pressure gradient, the multi-sensorassembly extending from a proximal end to a distal end portion, andcomprising: a sensor arrangement comprising a plurality of opticalsensors for measuring pressure, the sensors being positioned along alength of the distal end portion for simultaneously measuring pressureat a corresponding plurality of locations along said length; a pluralityof optical fibers, each fiber being coupled at a proximal end to anoptical input/output at the proximal end of the assembly and each fiberbeing optically coupled at a proximal end to an individual one of theplurality of optical sensors; and the distal end portion having adiameter suitable for introduction intraluminally through amicro-catheter.

A further aspect of the invention provides a method for measuring atransvalvular blood pressure gradient comprising: providing amulti-sensor wire; introducing and advancing the distal end portion ofthe multi-sensor wire into the heart and through the valve to bemonitored; positioning the pressure sensing means to place one or morepressure sensors at locations upstream of the valve and other sensors atlocations downstream of the valve to be monitored; and activating thesensors and obtaining data simultaneously from each sensor to obtain ablood pressure gradient during one or more time intervals.

Also provided is a method for measuring an intra-arterial or otherintra-vascular blood pressure gradient comprising: providing amulti-sensor wire; introducing and advancing the distal end portion ofthe multi-sensor wire into the arterial or other vascular region to bemonitored; positioning the pressure sensing means to place the pressuresensors at locations along the length of the region to be monitored;and, activating the sensors and obtaining data simultaneously from eachsensor to obtain a blood pressure gradient during one or more timeintervals.

The method may further comprise simultaneously obtaining flow velocitydata, and may comprise gathering blood pressure gradient and flowvelocity data over one or more cardiac cycles, and graphicallydisplaying the data from one or more of the sensors.

Thus, a small gauge, integrated multi-sensor apparatus or “multi-sensorwire”, e.g. in the form of a micro-catheter or steerable guidewire, isprovided that allows for direct measurement of a blood pressuredifferential or a blood pressure gradient, i.e. the comparison ofreal-time, direct blood pressure measurements at several locationssimultaneously, within heart ventricles, arteries and/or veins during aminimally-invasive intravascular intervention. In particular, amulti-sensor wire having a diameter of 0.89 mm or less, and preferably0.46 mm or less, provides for transvalvular pressure gradientmeasurements with minimal or negligible disruption of the heart valvefunction.

In addition, the multi-sensor wire allows for measurement of data toprovide indirect measurement of a cardiac blood output and, as aconsequence, estimation of the cardiac obstruction surface, i.e. thevalve area.

A multi-sensor wire according to embodiments of the invention thereforeprovides for novel methods for directly and precisely measuring atransvalvular pressure gradient in situ for any one of the four heartvalves. Beneficially, these methods provide for improvements to existingcardiovascular measurement techniques, i.e. the comparison of real-timedirect blood pressure measurements at several locations simultaneously,e.g. upstream, across and downstream of the heart valve, for each of thefour heart valves, during minimally-invasive (percutaneousintravascular) cardiovascular procedures.

Such methods provide measurements that enable cardiologists to moreaccurately quantify parameters or data indicative of the severity ofvalve disease, such as structural valve stenosis, and then promptlyidentify the diagnosis and provide the appropriate treatments topatients. In addition, following a heart valve procedure, such asvalvuloplasty or valve replacement, clinicians can assess or monitor thephysiologic performance of the new or repaired heart valve.

An apparatus comprising a multi-sensor assembly, a multi-sensor wire orguidewire, a system and methods according to embodiments of theinvention may also be used for directly measuring and monitoring a bloodpressure gradient within blood vessels, in real-time, usingminimally-invasive techniques.

It will also be appreciated that apparatus, systems and methods usingthe multi-sensor assembly have particular applications for thecardiovascular system; a similar multi-sensor wire system may also haveapplications in other systems of the body, i.e. for directly measuring afluid pressure gradient or flow in other biological fluids, for bothhuman and animal subjects, during a minimally-invasive procedure and/orfor evaluating prosthetic medical devices.

Thus, apparatus, systems and methods are provided that mitigate problemswith known methods and apparatus for measuring pressure gradients, andin particular provide for direct measurement of intravascular ortransvalvular pressure gradients and flow.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription, taken in conjunction with the accompanying drawings, ofembodiments of the invention, which description is by way of exampleonly.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, identical or corresponding elements in the differentFigures have the same reference numeral.

FIG. 1 illustrates schematically a longitudinal cross-sectional view ofan apparatus comprising a multi-sensor assembly comprising a pluralityof sensors according to a first embodiment of the present invention;

FIG. 2 illustrates schematically an enlarged longitudinalcross-sectional view showing details of the distal end portion of themulti-sensor wire illustrated in FIG. 1;

FIGS. 3A, 3B, 3C, 3D, 3E, 3F and 3G show enlarged axial cross-sectionalviews of the multi-sensor wire illustrated in FIGS. 1 and 2 takenthrough planes A-A, B-B, C-C, D-D, E-E, F-F and G-G respectively;

FIG. 4 illustrates schematically a system according to the firstembodiment, comprising a multi-sensor wire coupled to a control systemincluding a user interface;

FIG. 5 illustrates schematically a longitudinal cross-sectional view ofan apparatus comprising a multi-sensor wire assembly according to asecond embodiment of the present invention, with integrated elements forguiding (i.e. torquing and steering) the multi-sensor wire;

FIG. 6 illustrates schematically an enlarged longitudinalcross-sectional view of the distal end portion of the multi-sensor wireillustrated in FIG. 5;

FIGS. 7A, 7B and 7C show enlarged axial cross-sectional views of themulti-sensor wire illustrated in FIG. 6 taken through planes A-A, B-Band C-C respectively;

FIG. 8 shows a schematic of a human heart illustrating positioning ofthe multi-sensor wire of FIG. 1 during a method, according to a firstembodiment, for measuring the blood pressure gradient across the aorticheart valve;

FIGS. 9, 10 and 11 show corresponding schematics of a human heartillustrating positioning of the multi-sensor wire during methods,according to other embodiments, for measuring the blood pressuregradient across the mitral, tricuspid, and pulmonary heart valvesrespectively;

FIG. 12 shows a chart, known as a Wiggers diagram, showing typicalcardiac blood flow and pressure curves during a heart cycle for ahealthy heart;

FIGS. 13A, 13B and 13C show simplified schematics representing theaortic heart valve and left ventricle during measurement of atransvalvular pressure gradient through the aortic valve in a healthyheart, as the heart valve opens;

FIGS. 14A, 14B and 14C show similar simplified schematics representingthe aortic heart valve and left ventricle, in which shaded areasrepresent stenoses, during measurement of a transvalvular pressuregradient through the aortic valve using a multi-sensor wire according toan embodiment of the invention;

FIG. 15 shows a chart showing typical variations to the blood flow orpressure curves due to cardiac stenosis;

FIGS. 16A and 16B show sample pressure curves, measured over severalcycles, across bioprosthetic heart valves, of two different diameters,in a mechanical heart model, using a multi-sensor wire according to thefirst embodiment;

FIG. 16C shows a plot of the positive pressure difference between theventricular pressure and aortic pressure P1 (ventricle)-P4 (aorta),during several cardiac cycles, for each of the two types of valvestested; and

FIG. 17 illustrates schematically positioning of a multi-sensor wire, inthe form of micro-catheter or guidewire, within a vessel for pressuremeasurements by a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates a longitudinal cross-sectional view of an apparatus100 according to an embodiment of the invention, in the form of amulti-sensor wire, for measuring blood pressure, pressure gradients, andflow velocity, showing the internal structure and components. Themulti-sensor wire 100 has a suitable length and diameter forintravascular use, e.g. by introduction into the subject through anarrow gauge support catheter using a minimally-invasive procedure, aswill be described in detail below. Near the tip 33, a distal end portion101 of the a multi-sensor assembly comprises pressure and flow sensingmeans, which, in this embodiment, comprises an arrangement of aplurality of four optical pressure sensors 10 and an optical flow sensor20. Each sensor is coupled via a respective individual optical fiber 11to an optical input/output connector 112 at the proximal end 102, forcoupling of the multi-sensor wire 100 to a control system (see FIG. 4).An outer layer or covering layer 30 is provided, comprising a singlelayer or multilayer tubing, that forms a covering or cladding for themulti-sensor assembly. In this embodiment, the layer 30 comprises amicro-catheter (e.g. a flexible polymer tubing) having a lumen 106 thatsurrounds the bundle of optical fibers 11 and extends to the rounded tip33 at the distal end. The tip 33 is beneficially a soft flexible tip, asillustrated schematically, to facilitate insertion. At the proximal end102 of the multi-sensor wire, a thicker protective jacket or sleeve 32is also provided around layer 30. In the distal end portion, apertures12 are provided in the tubing 30, adjacent each of the sensors 10.Radio-opaque markers 14 are also provided at several locations along thelength of the distal portion 101 to assist in location of the sensorsduring measurements. Although the structure of the multi-sensor assemblyis shown in cross-section along its length from the connector 112 to thedistal tip 33, for simplicity, the internal structure of the connector112 is not shown. It will be appreciated that the optical fibers 11extend through the connector to optical inputs/outputs 113 of theconnector, as is conventional.

As shown in FIG. 1, the multi-sensor wire 100 optionally comprises, atthe proximal end, a hub 103 providing a Y connector to a side arm 104with a port 105 which gives access to the lumen, i.e. the cavity orspace, 106. Such a port is conventionally provided in a catheter orguidewire for flushing or filling the lumen with a fluid. The lumen 106extends the around optical fibers 11 along the length of the polymertubing 30 to the apertures 12, near each of the sensors 10, at thedistal end of the multi-sensor wire. In use, the port 105 in the sidearm provides the capability for flushing and filling the lumen 106 withfluid, e.g. normal saline solution, which assists in avoiding orremoving any air bubbles, particularly those which may become trapped inthe region of the sensors 10 near apertures 12, where bubbles mayinterfere with pressure measurements in the surrounding fluid.

FIG. 2 shows an enlarged longitudinal cross-sectional view of the distalend portion 101 of the multi-sensor wire 100 illustrated in FIG. 1. Asillustrated, the multi-sensor wire 100 is capable of measuring bloodpressure simultaneously at several points, in this case four points,using the four optic fiber-based pressure sensors 10 arranged along thelength 41 of the distal end portion of the multi-sensor wire. Forexample, as shown, the sensors are arranged at equal intervals along alength of the distal end portion 101, which length is determined by thedimension of the heart or vascular region to be monitored. Themulti-sensor wire 100 should preferably also be capable of measuringblood flow velocity since quantification of blood flow restriction isrelated to pressure difference and the blood flow velocity. It thereforeincludes an integral fiber-optic flow sensor 20 at a suitable positionin the distal end portion 101 to measure the blood flow velocity.

FIGS. 3A, 3B, 3C, 3D, 3E, 3F and 3G show enlarged axial cross-sectionalviews of the multi-sensor wire 100 taken through planes A-A, B-B, C-C,D-D, E-E, F-F and G-G respectively, of FIG. 1, illustrating the locationof the optical fibers 11, pressure sensors 10 and fiber-optic flowsensor 20 within the lumen 106 of polymer tubing 30. The polymer tubing30 is typically a flexible tubing comprising one or more layers ofpolymer materials, such as polyimide or polytetrafluoroethylene (PTFE),or other suitable bio-compatible or hemo-compatible materials having thedesired mechanical properties, and which allows the multi-sensor wire tobe introduced and slide easily through a support or guide catheter. Theradio-opaque markers 14 at the distal end allow the operator to locatethe position of the sensors of multi-sensor wire 100 within vascularregions or within the heart using a conventional medical imaging system,such as a fluoroscope. Apertures 12 in the polymer tubing 30 allowsensors 10 and 20 to be exposed for pressure and flow measurements inthe surrounding fluid, e.g. intravascular blood.

As illustrated schematically, each sensor 10 may be slightly larger indiameter than the optical fiber to which it is coupled. However, each ofthe optical pressure sensors 10 is a micro-sensor, preferably based onMOMS technologies, and more preferably they comprise a Fabry-Perotoptical cavity, where one of the two mirrors is a diaphragm.Low-coherence light is sent to the cavity from the controller throughthe input/output connector 112 via the optical fiber 11. Diaphragmmotions, due to pressure changes, are measured from spectral changesdetected in the reflected light received back at the detector. Suchsensors are described, for example, in U.S. Pat. Nos. 7,684,657 and7,689,071.

Optical pressure sensors of this type, which may be optically coupled toa control system, e.g. via optical fibers or other flexible lightguides, are substantially immune to humid conditions and toelectromagnetic parasitic interferences and noise involved with longelectric wires needed for electrical connections integrated withinguidewires. Moreover, optical pressure sensors 10 can be manufacturedwith smaller dimensions, e.g., with an outside diameter of 250 μm orless, compared to MEMS sensors. Each optical pressure sensor requirescoupling via a single optical fiber only rather than multiple wiresrequired for MEMS sensors.

Optical sensors are not susceptible to electronic drift that has beenreported for some MEMS sensors. Therefore, these optical pressuresensors allow the integration of an assembly of multiple pressuresensors 10, within multi-sensor wires 100 having an outside diameter of0.89 mm (0.035 inches) or less, and preferably, an outside diameter atthe distal end of 0.46 mm (0.018 inches) or less.

As illustrated in FIG. 1, the flow sensor 20 also comprises an opticalsensor, which advantageously comprises a novel optically coupledthermoconvection flow sensor, of a type which is described in moredetail in the above referenced copending U.S. provisional patentapplication No. 61/552,787. Preferably, this micro-flow sensorpreferably has a diameter similar to that of the optical fiber 11, i.e.125 μm, to which it is coupled. Other suitable micro flow sensors mayalternatively be used, e.g. a flow sensor either based on Doppler effector on temperature sensitive resistors.

Thus, in an exemplary embodiment, the outside diameter of themulti-sensor wire 100 would be 0.53 mm (0.021 inches) across thesections B-B and C-C and 0.46 mm (0.018 inches) across the sections D-D,E-E and F-F (see FIG. 2 and FIGS. 3A to 3F). That is, the multi-sensorwire has to accommodate all five fibers 11 and 21 at cross-section B-B,but narrows slightly towards cross-section F-F where only one fiber andsensor extends. The measurement range of the pressure sensors 10 wouldbe typically from −300 mmHg to +300 mmHg with an accuracy of +/−2 mmHg.The outside diameter of the optical fibers 11 and the pressure sensors10 would be 0.125 mm (0.005 inches) and 0.260 mm (0.010 inches)respectively. As illustrated in FIG. 1, the pressure sensors 10 aretypically located within a distance 41 of 4 to 7 centimeters (1.57 to2.76 inches) from the tip 33 at the distal end of the multi-sensor wire100.

In this embodiment, each pressure sensor 10 is optically coupled to anindividual optical fiber 11, e.g. by adhesive bonding or other suitablebonding method. If necessary, a length of protective tubing, e.g.polyimide, may be provided around the optical sensor and a short length,e.g. a few mm, at the end of the optical fiber, to protect the bondedregion and/or to provide mechanical reinforcement. Using a suitablemanual or automatic alignment and adhesive bond, the bundle ofindividual fibers are aligned so that the sensors are arranged toprovide the required spacing between each sensor. The total outsidediameter of the pressure sensors 10 protected by the tubing would beabout 0.30 mm (0.012 inches). A multi-sensor wire 100 would typically beprovided with a rounded distal tip 33, which may be a soft flexibleJ-tip. The distance from the distal tip 33 of the multi-sensor wire 100to the distal end of the jacket 32 would typically be about 1.6 m (63inches).

As illustrated in FIG. 4, a multi-sensor wire system comprises themulti-sensor wire apparatus 100 and a system controller 150. The systemcontroller 150 has a user interface front panel 152 and a graphical userinterface 151 for displaying simultaneously, in real-time, chartsshowing the measurement data from the pressure sensors 10 at eachlocation and from the fiber-optic flow sensor 20. The user interfaceincludes controls 154 on the front panel 152 and/or as part of a touchscreen 151. The multi-sensor wire 100 is attached to the system userinterface 150 via the multi-sensor wire input/output connector 112 andthe user interface input/output port 153.

The control system 150 includes a processor, with appropriate hardwareand software for controlling the system and obtaining data indicative ofpressure, flow and any other measured parameters from the sensors 10 and20, and displaying or storing data in a desired format. It also includesa light source, from which light is sent to each optical pressure sensor10 via its respective fiber 11, and a detection system for detectingchanges in the light reflected back from the Fabry-Perot sensors, whichare indicative of pressure values. Similarly, light is sent down therespective fiber 21 to the flow sensor 20, and changes in the lightreceived back at the detector are indicative of thermal changesdependent on flow velocity. If required, the controller 150 may includea separate higher intensity light source and detector for the opticalflow sensor 20. If other electrical sensors or peripherals are used, thecontroller includes the appropriate electrical connections andelectronics. The control system 150 may be a stand-alone unit, anoptical control unit run from a PC, or part of a system integrated withother equipment used for cardiology procedures.

Methods for measurement and monitoring of transvalvular pressuregradients and flow for each heart valve, and for assessing or monitoringother blood vessels, will be described in detail in the followingsections.

However, the use of the optical multi-sensor wire 100 in the form of amicro-catheter will first be described very briefly, so as to introducea second embodiment in which the multi-sensor wire takes the form of aguidewire.

In summary, in use of the optical multi-sensor wire 100 in the form of amicro-catheter, for measurement of intravascular or transvalvular bloodpressure gradients and flow, a cardiologist would first introduce aguide/support catheter to allow the optical multi-sensor wire to bequickly introduced into the region of interest. A guide catheter mayalready be in place for other cardiac procedures. If not,conventionally, this would involve first introducing a conventionalguidewire, which can be torqued using established techniques, for otherintravascular or cardiac procedures. Such a guidewire typically includesa J tip and has suitable flexibility and torque characteristics to allowit to be steered and guided to position the type in the region ofinterest, e.g. near the heart valve or stenosed region. Thesupport/guide catheter is then introduced over the guidewire. Theguidewire is then withdrawn, to allow subsequent introduction of theoptical multi-sensor wire through the support catheter, and into theregion of interest for pressure gradient and flow measurements. Theradio-opaque markers on the multi-sensor wire or micro catheter allowfor monitoring of the location of the multi-sensor wire and its sensors,while it is positioned in the region of interest, e.g. in the bloodvessels or heart.

Once the array of sensors is positioned appropriately, and themulti-sensor wire is coupled to the control system, the sensors areactivated to gather pressure and/or flow velocity data simultaneouslyfrom each sensor, for example, during one or more time intervals in acardiac cycle, or over several cycles. Alternatively, while the sensorsare activated, a pressure gradient data may be obtained simply andquickly from one position, and then sensor array may be moved to adifferent position for another measurement to explore the region ofinterest, while providing instantaneous pressure gradient and cardiacflow information. In some situations, it may be desirable to activatethe sensors before positioning the multi-sensor wire to assist infinding the region of interest, e.g. a region of maximum restriction.

If a guide/support catheter is not already in place for otherprocedures, it is desirable to have a self-guiding multi-sensor wire.

Thus, a multi-sensor wire 120, according to a second embodiment of thepresent invention, is illustrated in FIGS. 5, 6 and 7, and takes theform of a guidewire, comprising integrated torque steering elements forguiding the multi-sensor wire, i.e. a mandrel, coil and J tip, similarto those used in a conventional guidewire. Referring to FIG. 5, allcomponents that are similar to those of the multi-sensor wire 100 shownin FIGS. 1 to 4 are shown with the same reference numerals.

Thus, the multi-sensor wire 120 of the second embodiment differs fromthat of the first embodiment in comprising a central core-wire ormandrel 31, and a coiled outer layer 35, i.e. instead of the polymertubing 30 of sensor wire 100, the outer layer is provided by a fine wirecoil 35 made of metal alloy. A protective jacket 32 is provided on theproximal end. The coil 35, along with the mandrel 31, provides thesteerable and torquable characteristics of the multi-sensor wire 120 sothat is capable of being shaped or flexed to traverse vascular regionsin the same manner as a conventional guidewire. The mandrel, coil andthe J-shape distal tip 33 allows for the multi-sensor wire to besteerable using a conventional torque device 13 mounted on the proximalshaft.

As shown in the enlarged longitudinal cross-sectional view in FIG. 6, atthe distal end 121, the multi-sensor wire 120 comprises four opticalpressure sensors 10 similar to those of the embodiments described above.Instead of an optical flow sensor, it integrates a flow sensor 25 in theform of a temperature sensitive resistor, i.e. a resistivethermoconvection sensor, or thermistor such as used in a Swann-Ganzcatheter. For an electrical flow sensor of this type, a pair of electricwires 23 is provided within the coil 35 to connect the blood flow sensor25 to the system user interface 150 via the multi-sensor wire connector112. FIGS. 7A, 7B and 7C are enlarged axial cross-sectional views of themulti-sensor wire 120, taken at planes A-A, B-B and C-C respectively,illustrating the location of the optical fibers 11, mandrel 31,electrical wires 23 and pressure sensors 10 within the coil 35.

The multi-sensor wire 120 preferably has an outside diameter similar tothat of the multi-sensor wire 100, i.e. an outside diameter of 0.89 mmor less and preferably 0.46 mm or less near the distal end.

Since the multi-sensor wire 120 is steerable, it can be introducedquickly for pressure gradient and flow measurements, without the needfor first introducing a guide catheter. Measurement of pressuregradients may be made as the guidewire is advanced.

In a multi-sensor wire 130 according to another embodiment (notillustrated), instead of an all optical sensor embodiment described withreference to FIGS. 1 to 4, the optical flow sensor 20 may insteadcomprise a conventional resistive thermoconvection sensor 25, similar tothat used in the second embodiment, which is coupled to an electricalconnector of the control system by a pair of electrical wires 23 insteadof optical fiber 21.

In yet another embodiment (not illustrated), an apparatus may beprovided similar to that shown in FIG. 5, but using an optical flowsensor. This provides an all-optical multi-sensor wire implementation,and eliminates the need for an electrical connection.

While several embodiments are described and illustrated, by way ofexample, comprising four optical micro-pressure sensors and an opticalflow sensor, it will be appreciated that other embodiments may beprovided with different numbers and types of pressure and flow sensors.However, at least two pressure sensors are needed for measuring apressure differential, and preferably, four or more pressure sensors areprovided for measuring pressure gradients, e.g. two on each side of aheart valve or vascular region of interest. The spacing of the sensorsalong the distal portion of the multi-sensor wire may be selected toposition the sensors at the suitable locations, but typically forcardiac applications, may be positioned for measuring a gradient along alength of about 4 cm to 7 cm, e.g. with four equally spaced sensors. Forsimultaneous measurement of flow at least one flow sensor is alsorequired. Advantageously, optical pressure sensors eliminate the needfor multiple long electrical connections and associated reliabilityissues, electromagnetic noise and interference issues. Radio-opaquemarkers may be provided on the sensors or at intervals along themulti-sensor wire as appropriate, but alternatively other suitablemarkers may be provided for use with other imaging modalities. Ifrequired, a port is provided for filling or flushing the lumen of theapparatus, e.g. a hub with a side arm port shown in FIG. 1, otherconventional arrangement.

While it may be desirable to provide a greater number of sensors, e.g.eight or more, the number will be limited by the maximum permissiblediameter of the multi-sensor wire, and the size of the sensors andoptical fibers, and may be dependent on other factors such as requiredflexibility or stiffness of the multi-sensor wire. While Fabry-PerotMOMS pressure sensors are described, in alternative embodiments, othersuitable miniature optical pressure sensors may be used. Optionally,other sensors, such as a temperature sensor, or a combined flow andtemperature sensor may be provided.

If the multi-sensor wire does not include an integral flow sensor, thecardiac flow velocity may alternatively be measured conventionally by aseparate Swan-Ganz catheter, by Doppler echography, by a Doppler effectflow sensor, or by the method of Fick.

Although a single optical connector 112 is shown for the input/outputfor each of the five of optical fibers 11, in other embodiments, analternative connector or coupling arrangement may be provided. Themulti-sensor wire connector 112 and the user interface port 153 maycomprise several individual optic fiber connectors, instead of a singlemulti-fiber connector. In yet other embodiments, multiple sensors 10 and20 may be coupled, via a multiport optical coupler at some point alongthe multi-sensor wire, to a single fiber, with multiplexing of signalsfrom multiple sensors. The connector 112 may optionally includecircuitry allowing wireless communication of control and data signalsbetween the multi-sensor wire 100 and the system controller 150 and userinterface 151. Optionally one or more electric connectors for peripheraldevices, or for additional or alternative electrical sensors, may beprovided.

It will also be appreciated that for medical or veterinary applications,the multi-sensor wire should be fabricated from suitable biocompatiblematerials, and provided in a suitable sterile packaged form. Typicallythe multi-sensor wire assembly is provided for single use, and isdisposable. Thus, cost and environmental considerations may be importantin selecting appropriate components and materials.

Measurement of Transvalvular Pressure Gradient Across the Aortic,Mitral, Tricuspid and Pulmonary Valves of the Heart

A method, according to a first embodiment of the present invention, formeasuring and monitoring the blood pressure gradient across the aorticvalve 211, i.e. the aortic transvalvular pressure gradient, in a humanheart 200 using a multi-sensor wire 100 according an embodiment, such asdescribed with reference to FIGS. 1 to 4, is described below withreference to FIG. 8. A conventional guidewire is first inserted into aperipheral artery, such as the femoral or carotid, using knowntechniques, and advanced through the ascending aorta 210. A supportcatheter 160 is then slid over the guidewire. The operator then advancesand positions the support catheter 160 in proximity to the aortic valve211, using visualization devices such as radio-opaque markers on itsdistal end. The operator then replaces the guidewire by the multi-sensorwire 100 in the lumen of the support catheter 160. The operator advancesand positions the distal end of the multi-sensor wire 100 into the leftventricle 212 using visualization devices such as radio-opaque markers14 on its distal end. Once the multi-sensor wire 100 is properlypositioned, the system measures the transvalvular pressure gradient ofthe aortic valve 211. As illustrated schematically in FIG. 8, threepressure sensors 10 are positioned in the left ventricle 212 and onepressure sensor is positioned in the aorta 160 just downstream of theaortic valve 211, to allow simultaneous measurements of pressure at fourlocations upstream and downstream of the valve. A series of measurementsmay be taken during several cardiac cycles. Although not illustrated inFIG. 8, a flow sensor 20 may also be provided for simultaneous flowmeasurements. Measurements results may be displayed graphically, e.g. asa chart on the graphical user interface 151 of the system controller 150(see FIG. 4) showing the pressure gradient and flow. The control systemmay provide for multiple measurements to be averaged over severalcycles, and/or may provide for cycle-to-cycle variations to bevisualized. If appropriate, the multi-sensor wire may be alternativelypositioned, e.g. to make measurements simultaneously at four differentlocations, for example with two pressure sensors positioned each side,i.e. upstream and downstream respectively of the aortic valve 213. Thus,the operator can quickly and easily obtain transvalvular pressuregradient measurements. Measurements may be made, for example, before andafter valve replacement or valve repair procedures.

A method, according to a second embodiment, to measure and monitor theblood pressure gradient across the mitral valve 213, i.e. the mitraltransvalvular pressure gradient, in a human heart 200 is described belowand illustrated by FIG. 9. A guidewire is first inserted into aperipheral large vein, such as the inferior vena cava 220, using knowntechniques, and advanced through the ascending vein 220 to the rightatrium 221. The support catheter 160 is then slid over the guidewire.The operator then advances the support catheter 160 to the right atrium221 and then crosses the septum to position the support catheter 160 inthe left atrium 214 near the mitral valve 213, using known techniques.The operator then replaces the guidewire by a multi-sensor wire 100 inthe lumen of the support catheter 160. The operator advances andpositions the distal end of the multi-sensor wire 100 into the leftventricle 212, using visualization devices such as radio-opaque markers14 on its distal end. Once the multi-sensor wire 100 is properlypositioned, the system measures and displays the transvalvular pressuregradient of the mitral valve 213.

A method, according to a third embodiment, to measure and monitor theblood pressure gradient across the tricuspid valve 222, i.e. thetricuspid transvalvular pressure gradient, in a human heart 200, isdescribed below and illustrated by FIG. 10. A guidewire is firstinserted into a peripheral large vein, such as the inferior vena cava220, using known techniques, and advanced through the ascending vein 220to the right atrium 221. The support catheter 160 is then slid over theguidewire. The operator then advances and positions the support catheter160 in proximity to the tricuspid valve 222, using visualization devicessuch as radio-opaque markers on its distal end. The operator thenreplaces the guidewire by a multi-sensor wire 100 in the lumen of thesupport catheter 160. The operator advances and positions the distal endof the multi-sensor wire 100 into the right ventricle 223 usingvisualization devices such as radio-opaque markers 14 on its distal end.Once the multi-sensor wire 100 is properly positioned, the systemmeasures and displays the transvalvular pressure gradient of thetricuspid valve 222.

Similarly, in a fourth embodiment, a method to measure and monitor theblood pressure gradient across the pulmonary valve 224 (i.e. thepulmonary transvalvular pressure gradient) in a human heart 200 isdescribed below and illustrated by FIG. 11. The operator advances andpositions the distal end of the multi-sensor wire 100 into the rightventricle 223 using visualization devices such as radio-opaque markers14 on its distal end as described above. The operator then furtheradvances the support catheter 160 in proximity to the pulmonary valve224. The operator then further advances and positions the distal end ofthe multi-sensor wire 100 into the pulmonary artery 225. Once themulti-sensor wire 100 is properly positioned, the system measures anddisplays the transvalvular pressure gradient of the pulmonary valve 224.

The function of the heart is to move de-oxygenated blood from the veinsto the lungs and oxygenated blood from the lungs to the body via thearteries. The right side of the heart collects de-oxygenated blood inthe right atrium 221 from large peripheral veins, such as, the inferiorvena cavae 220. From the right atrium 221 the blood moves through thetricuspid valve 222 into the right ventricle 223. The right ventricle223 pumps the de-oxygenated blood into the lungs via the pulmonaryartery 225. Meanwhile, the left side of the heart collects oxygenatedblood from the lungs into the left atrium 214. From the left atrium 214the blood moves through the bicuspid valve 213 into the left ventricle212. The left ventricle 212 then pumps the oxygenated blood out to thebody through the aorta 210.

Throughout the cardiac cycle, blood pressure increases and decreasesinto the aortic root 210 and left ventricle 212, for example, asillustrated by the pressure curves 330 and 340, respectively, in FIG.12, which shows curves typical of a healthy heart. The cardiac cycle iscoordinated by a series of electrical impulses 310 that are produced byspecialized heart cells. The ventricular systole 301 is the period oftime when the heart muscles (myocardium) of the right 223 and leftventricles 212 almost simultaneously contract to send the blood throughthe circulatory system, abruptly decreasing the volume of blood withinthe ventricles 320. The ventricular diastole 302 is the period of timewhen the ventricles 320 relax after contraction in preparation forrefilling with circulating blood. During ventricular diastole 302, thepressure in the left ventricle 340 drops to a minimum value and thevolume of blood within the ventricle increases 320.

FIGS. 13 and 14 are simplified schematics of the aortic heart valve 211and left ventricle 212, illustrating the concept of aortic transvalvularpressure gradient as measured by the multi-sensor wire 100 using themethod of the first embodiment described above, for a healthy heart andfor a heart with stenoses 231, 232 and 233. In this particular example,the aortic transvalvular pressure gradient is the blood pressuremeasured by sensors at locations P1, P2, P3 and P4 within the leftventricle 212 and the aortic root 210.

The left heart without lesions, illustrated on FIG. 13, would generateaortic and ventricular pressure curves similar to curves 330 and 340,respectively, in FIG. 12. However, the heart illustrated in FIG. 14 hasmultiple sites of potential blood flow 230 obstructions 231, 232, and233. In some cases, the operator of the multi-sensor wire 100 might wantto measure the blood pressure at several locations, P4 and P3, withinthe root of the aorta 210 in order to assess a supravalvular aorticstenosis 231 (most commonly an anomalous congenital membrane located inthe aortic root).

The cardiac hemodynamic data collected from a patient's heart allow aclinician to assess the physiological significance of stenosis lesions.The aortic and ventricular pressure curves from a patient's heart arecompared with expected pressure curves. FIG. 15 illustrates typicaldifferences between the aortic 330 and ventricular 340 pressure curvesdue to intracardiac obstructions. Some of those variations include themaximal difference 305 and the peak-to-peak difference 306 betweencurves 330 and 340. The area 307 between the aortic pressure curve 330and ventricle pressure curve 340 is also used to assess thephysiological significance of stenosis lesions. The difference betweenthe amplitude 303, 304 of the aortic 330 and ventricle 340 pressurecurves is also key information for the clinician.

The medical reference literature relating to cardiac catheterization andhemodynamics provides different possible variations of the aortic 330and ventricular 340 pressure curves along with the possible causes inorder to identify the proper medical diagnosis. For example, cardiachemodynamic curves, such as shown in FIG. 15, along with analysis of thecurves, are provided on pages 647 to 653 of the reference book entitledGrossman's cardiac catheterization, angiography, and intervention byDonald S. Baim and William Grossman.

Prototype multi-sensor wires 100 based on the first embodiment, asillustrated schematically in FIG. 1, were assembled and tested. Themulti-sensor assembly was fabricated comprising four Fiso FOP-M260pressure sensors, each sensor 10 being bonded to an individual opticalfiber 11, and the multi-sensor assembly was enclosed within a tri-layerpolymer tubing of 0.76 mm outside diameter (0.028″), with apertures 12near each sensor 10. Each sensor has an outside diameter (OD) of 0.260mm). Each sensor was bonded to an individual 0.125 mm OD optical fiber.The four sensors and their respective optical fibers were assembled toprovide a 2 cm spacing between pressure sensors along a length of thedistal end of the multi-sensor wire near the distal tip. During theinitial in-vitro laboratory testing, the prototypes demonstrated toprovide accurate real-time pressure gradient measurements in staticwater columns. The sensors were calibrated to measure a pressure rangefrom −300 mmHg to 300 mmHg, with an accuracy of ±2 mmHg.

Subsequently, the prototype multi-sensor wire comprising 4 pressuresensors was tested in a simple activation pulse duplicator system(Vivitro Systems), which is a heart model that simulates cardiac pulsepressures and flows found in the left ventricle and the aorta of a humancardiac system. The duplicator system was equipped with bioprostheticvalves, which were the trileaflet pericardial variety (Perimount 2900from Carpentier-Edwards). Valves of two different diameters were used inthe testing: 29 mm, which simulates a normal healthy valve, and 19 mm,which simulates a valve with reduced aortic valvular area. Themulti-sensor wire was inserted through the valve opening such that apressure sensor P1 was located in the ventricle cavity and anotherpressure sensor P4 was located in the aortic cavity. FIGS. 16A and 16Bshow curves 330, 340 representing the pressure readings from pressuresensors P4 (aorta) 330 and P1 (ventricle) 340, for the 29 and 19 mmvalves, respectively. A person skilled in the art will observe that thepressure difference between the pressures P1 and P4, for the ventricleand aorta respectively, for the 19 mm diameter valve during the systolicphase is greater than that of the 29 mm valve, and indicates reducedvalvular area.

For comparison of the textbook hemodynamic curves shown in FIGS. 12 and15, with the experimentally measured curves shown in FIGS. 16A and 16B,the corresponding pressure traces have been labeled with the samereference numbers, i.e. in each Figure shows an aortic pressure trace330 and the ventricular pressure trace 340. In each of the plots shownin FIGS. 16A and 16B, the third curve 345 represents the pressure curvefor another sensor P2 located 2 cm from P1 (ventricle). The curve forthe other sensor P3 is not shown.

FIG. 16C shows another plot of data from the same experiment. Thisfigure shows the pressure difference P1 (ventricle) minus P4 (aorta)measured by the two pressure sensors located in the ventricle and aorta,respectively, for each of the two valves of different diameter. Thedifferential pressure measurements shown in FIG. 16C emphasize thereduced performance, evidenced by the much larger peak transvalvularpressure difference, for the 19 mm diameter valve (curve 350) relativeto the 29 mm valve (curve 360).

It is apparent from these preliminary results that the multi-sensor wirecomprising a plurality of optical pressure sensors provides for opticalmeasurement of pressure gradients in an appropriate pressure range andwith a suitable sensitivity, accuracy and resolution for measurement ofin vivo blood pressure gradients and for obtaining data for aortic andventricular pressure curves. These initial results demonstrate, prior toin vivo testing and pre-clinical trials, that the multi-sensor wire iseffective for measurement of aortic and ventricular pressure curves forassessing operation of bioprosthetic heart valves in a heart model.

In summary, an apparatus, system and methods according to embodiments ofthe invention are described for simplification of the measurement of atransvalvular pressure gradient for each of the four heart valves. Inparticular, by using multiple miniaturized sensors, it is possible tomeasure, simultaneously, the pressure of one part, or the other, of adysfunctional valve while traversing it with a micro-catheter ofdiameter 0.89 mm (0.035″) or less, comprising a plurality, e.g. fourmicro pressure sensors. Consequently, one or several sensors can belocated on one side or the other of the valve, thus permittinginstantaneous measurement, e.g. in the region of maximal obstruction.The small physical size of the device reduces interference with valveoperation when it is passes through or is inserted through a valve, e.g.provides less interference with the movement of the valve and/or lessperturbation of the transvalvular pressure gradient. Moreover, itenables measurements that permit the determination of whether thestenosis is strictly associated with the valve or not, to a subvalvularstenosis (e.g. sub-aortic hypertrophic stenosis) or supravalvularstenosis. For example, the severity of the aortic stenosis is definedclassically by a mean pressure gradient of >50 mmHg or a valvularsurface of <0.75 cm².

In particular, the sensor means may comprise a plurality of pressuresensors, or an array of sensors, in a distal region, or at the distalend, of a guidewire, which is insertable, for example, into a lumen ofan artery, or a chamber of the heart. Beneficially the pressure sensormeans comprises optical sensors coupled to fine gauge optical fibersthat may be introduced into the body with the guidewire, through acatheter. Thus, signals indicative of pressure may be optically detectedand eliminate the need for electrical connections to be made along theguidewire, unless other types of electrical sensors are included.Optionally, the apparatus may further comprise temperature sensing meansor other sensors of different types. For example, one or more electricalsensors may also be included to allow for measurement of relatedparameters, e.g. temperature measurements and/or flow measurementsmeasured by resistive sensing means, for example.

For pressure gradient measurements, it will be appreciated that,ideally, data is gathered simultaneously from each of the plurality ofpressure sensors, and optionally with simultaneous data from othersensors, e.g. a flow sensor. However, it will be appreciated the systemmay also be configured to allow for data to be selectively gatheredand/or displayed, as needed, from one or more pressure sensor, flowsensor, temperature sensor or other sensors as appropriate, and to allowfor data to be graphically displayed over one or more cardiac cycles orother time intervals.

Thus, apparatus according embodiments of the invention provide a medicalspecialist with a device that permits simultaneous measurements ofpressure at several points in the region of interest. Multiple pressuresensors provide for measurement of a pressure gradient in real time. Forinstance, such a multi-sensor wire or guidewire equipped with aplurality of pressure sensors could evaluate pressure differenceupstream and downstream a heart valve. Heart valve degradation could beevaluated based on the measured pressure difference. There are severalother examples where simultaneous measurement of pressure at severallocations would be advantageous over a single point measurement. Forinstance such devices could evaluate heart artery blockage, urinarytrack blockage, thickening of the heart wall (ventricular hypertrophy),for example. Beneficially, the multi-sensor wire enables measurements tobe made that allow the cardiac output and valvular area to be determinedsimultaneously, and more simply and safely compared with existingapparatus and techniques.

The length and diameter of the multi-sensor wire may be selecteddependent on the application for which pressure, flow, or temperature isto be measured. For example, cardiovascular applications, such astransvalvular measurements, sensors may be arranged, e.g. equallyspaced, along a length of typically 4 cm to 7 cm of the distal endportion of the sensor wire, depending on the size of the heart or regionin which measurements are to be made. Other arrangements of the sensorsmay be desirable depending on the dimensions of the region wheremeasurements are to be made.

In the embodiments described above, the plurality of optical pressuresensors in the multi-sensor assembly are arranged at locations along thedistal end portion so that their relative positions are known, i.e.determined by their spacings along the length of the distal end portion.While the distal portion is sufficiently flexible for introductionintravascularly, relative movement of the plurality of sensors isconstrained. Thus, when gathering data simultaneously from the sensors,there is greater certainty in the relative location of each of thesensors in the region of interest vs. sequential measurements indifferent locations using a single sensor guide wire. This isparticularly useful for measuring pressures and flows with the heart,where higher flows and turbulence tends to cause excessive movement ofsingle sensors located at the end of a sensor wire. While theembodiments described above focus on measurement and monitoring oftransvalvular blood pressure gradients and flow, it will be appreciatedthat the multi-sensor wire apparatus and methods may be adapted ormodified to measure pressure gradients and flow in the blood vessels.When a multi-sensor wire is used for other applications, its outsidediameter may have to be reduced to 0.36 mm (0.014″) or less. Thearrangement of the sensors, e.g. their number, location, and spacing,and the accuracy and pressure measurement range of the pressure sensorsmay also have to be tailored to meet the specific requirements of themedical application.

For example, the apparatus may be provided comprising a plurality ofoptical pressure sensors 10 in the form of a multi-sensor wire 100 thatmay be introduced into a vessel through a micro-catheter or as amulti-sensor equipped steerable guidewire. Such an apparatus may beconfigured to measure pressure simultaneously at several locations alonga length of a distal portion of the guidewire, as shown schematically inFIG. 17. FIG. 17 shows a simplified schematic of a vessel, such as anartery 401, with multiple stenoses 431, which are restrictions to theblood flow 430. The blood pressure is measured by a multi-sensor wire100 at four different locations P1, P2, P3 and P4 simultaneously in thevessel.

It will also be appreciated that embodiments of the multi-sensor wiresystem, apparatus and methods may also have applications for measuringfluid pressures, gradients and flows in other systems of the body, suchas the urinary tract, biliary tract or venous system, of animal or humansubjects.

In some embodiments all-optical micro-sensors for measurement of bothpressure and flow are used to avoid the need for electrical connectionsaltogether, which reduce issues of electromagnetic noise andinterference and signal reliability. In other embodiments, opticalpressure sensors and one or more electrical sensors, e.g. for flow ortemperature, may be combined.

It will be appreciated that in the context of this description, the term“wire” in “multi-sensor wire” or “multi-sensor guidewire” is intended torefer to apparatus having a small diameter and elongated form similar toconventional single sensor wires and guidewires, such as used forcardiac catheterization procedures: i.e. the term “wire” is not intendedto be limited to a conventional metallic wire and in a more generalsense encompasses an element in the form of a filament, strand, cable orother long, thin (i.e. small diameter) element, so as to convenientlydescribe the form of a multi-sensor apparatus. As described above, insome embodiments, the multi-sensor wire comprises an assembly of aplurality of optical pressure sensors, which are optically coupled byflexible light guides such as optical fibers, to the opticalinput/output at proximal end of the apparatus, without electricalcomponents. These components may be integrated with conventionalsteerable guidewire components. In some embodiments, an electricalsensor with conventional wired electrical connections (i.e. usingconventional conductive metallic wires) may be included. In someembodiments, the sensor apparatus may alternatively be referred to as amulti-sensor device, a multi-sensor diagnostic wire or multi-sensorguidewire, for example.

INDUSTRIAL APPLICABILITY

Systems, apparatus and methods according to embodiments of the inventionare provided that simplify the measurement of pressure gradients orpressure differences, and/or flow, particularly a transvalvular pressuregradient. Such measurements enable key cardiac parameters to bedetermined using an improved minimally-invasive procedure. Thecardiologist is provided with a tool for more quickly, simply andreliably measuring and monitoring transvalvular pressure gradients, forexample, before and after valve repair or replacement procedures.

It will be apparent that the system and apparatus also provide formeasurement of pressure gradients for research, testing and assessmentof the operation of artificial hearts, prosthetic heart valves, andother synthetic devices for medical use.

In particular, using a multi-sensor device having a diameter of 0.89 mm(0.035″) or less, comprising, for example, four pressure sensors and aflow sensor, it is possible for the cardiologist to measure,simultaneously, the pressure at several points from one side to theother of a dysfunctional valve while the sensors of the multi-sensordevice are positioned through the valve. For example, if the diameter ofthe aorta is known, use of a multi-sensor wire capable of simultaneouslymeasuring a pressure gradient and flow, allows for evaluation of thecardiac output and, as a consequence, estimation of, for example, thevalve area or lumen area.

One or several sensors can be localized on each side of the valve,permitting instantaneous measurement of a pressure gradient and flow,e.g. in the region of maximal obstruction. Miniaturization of themulti-sensor device, e.g. having a distal portion of 0.46 mm (0.018″)diameter or less, means that the presence of the device through thevalve has minimal or negligible effect on the movement of the valve andhas minimal or negligible repercussions on the measurement of thetransvalvular pressure gradient. For example, it permits thecardiologist to make a rapid determination of whether the stenosis isstrictly associated with the valve or not, or to a sub-valvularobstruction, e.g. sub-aortic hypertrophic stenosis.

A multi-sensor wire or guidewire, system and methods according toembodiments of the invention may also be used to obtain pressuremeasurements that can be used to evaluate, in addition to the severityof stenosis of a heart valve, evaluate the severity of stenoses ofsurrounding regions of the valve, known as subvalvular and supravalvularstenoses. Such evaluation would permit the clinician to determine ifvalve stenosis is the major impediment to blood flow and warrant a valverepair or replacement.

Although embodiments of the invention have been described andillustrated in detail, it is to be clearly understood that the same isby way of illustration and example only and not to be taken by way oflimitation, the scope of the present invention being limited only by theappended claims.

The invention claimed is:
 1. An apparatus for measuring a blood pressuregradient during a minimally invasive intravascular or cardiacintervention comprising: a multi-sensor assembly contained within atubular covering layer, the tubular covering layer comprising amicro-catheter or a coil of a steerable guidewire, the tubular coveringlayer extending between a proximal end and a distal end, and the distalend comprising a flexible distal tip; the multi-sensor assemblycomprising: a plurality of optical fibers and a plurality of opticalsensors, each optical fiber having a proximal end and a distal end, eachindividual one of the plurality of optical sensors being attached andoptically coupled to the distal end of a respective individual one ofthe plurality of optical fibers; the plurality of optical fibers beingassembled as a bundle with distal ends of the plurality of opticalfibers arranged to form a sensor arrangement wherein said plurality ofoptical sensors have sensor locations spaced apart lengthwise from eachother; the multi-sensor assembly extending within the tubular coveringlayer from the proximal end into a distal end portion adjacent thedistal end, with the sensor arrangement, comprising said plurality ofoptical sensors, being located within the distal end portion of thecovering layer for measuring pressure at respective sensor locationsspaced apart along a length of the distal end portion; and the proximalend of each one of the plurality of optical fibers being opticallycoupled to an optical input/output for connection to a control system;an aperture in the covering layer adjacent each optical sensor; saidsensor arrangement providing for a measurement of pressure at eachsensor location for determination by the control system of a bloodpressure gradient; and at least the distal end portion of the tubularcovering layer having an outer diameter suitable for introductionintravascularly or percutaneously.
 2. The apparatus of claim 1 whereinthe tubular covering layer comprises the coil of a steerable guidewire,and further comprising torque steering components comprising a core-wireextending axially through the coil from the proximal end, through saidbundle of optical fibers, to the distal end of the coil.
 3. Theapparatus of claim 1 wherein the tubular covering layer comprises thecoil of a steerable guidewire, and further comprising torque steeringcomponents of the guidewire comprising a core-wire extending axiallythrough the coil from the proximal end to the distal end, themultisensor assembly comprising said plurality of optical fibers andplurality of optical sensors being assembled around the core-wire andsecured thereto, and the multisensor assembly extending through the coilfrom the proximal end into the distal end portion to position the sensorarrangement in the distal end portion with said aperture adjacent eachoptical sensor.
 4. The apparatus of claim 3, wherein the optical sensorscomprise Micro-Opto-Mechanical Systems (MOMS) pressure sensors.
 5. Theapparatus of claim 4, wherein the MOMS sensors comprise Fabry-Perot MOMSsensors.
 6. The apparatus of claim 3, wherein the sensor arrangementfurther comprises at least one of a flow sensor and a temperaturesensor.
 7. The apparatus of claim 6, wherein the flow sensor comprisesan optical flow sensor and an optical fiber coupling said optical flowsensor to the optical input/output.
 8. The apparatus of claim 7, whereinthe optical flow sensor comprises an optical thermoconvection flowsensor.
 9. The apparatus of claim 6, wherein the flow sensor comprisesan electrical flow sensor and the multi-sensor assembly furthercomprises electrical connections coupling the electrical flow sensor toan electrical input/output at the proximal end.
 10. The apparatus ofclaim 3 wherein the distal end portion of the coil containing the sensorarrangement has an external diameter of 0.89 mm or less.
 11. Theapparatus of claim 3 wherein the distal end portion of the coilcontaining the sensor arrangement has an external diameter of 0.46 mm orless.
 12. The apparatus of claim 3, wherein said optical input/output ofthe multi-sensor assembly comprises part of a connector for opticallycoupling the multi-sensor assembly to the control system.
 13. Theapparatus of claim 1, wherein the tubular covering layer comprises amicro-catheter having a lumen, and said bundle of optical fibers extendsthrough the lumen of the micro-catheter from the proximal end into thedistal end portion, positioning the sensor arrangement in the distal endportion of the micro-catheter with said aperture adjacent each opticalsensor, and wherein the distal end portion containing the sensorarrangement has an outside diameter of 0.89 mm or less.
 14. Theapparatus of claim 13, wherein the optical sensors compriseMicro-Opto-Mechanical Systems (MOMS) pressure sensors.
 15. The apparatusof claim 13, wherein the MOMS sensors comprise Fabry-Perot MOMS sensors.16. The apparatus of claim 13, wherein the sensor arrangement furthercomprises a sensor for measuring at least one of flow and temperature.17. The apparatus of claim 13, wherein the sensor arrangement furthercomprises an optical thermoconvection flow sensor.
 18. The apparatus ofclaim 13, further comprising at least one radiopaque marker for locatingthe sensor arrangement.
 19. The apparatus of claim 13, wherein thedistal end portion of the micro-catheter has an external diameter of0.46 mm or less.
 20. The apparatus of claim 1, configured for measuringa transvalvular blood pressure gradient within the heart during aminimally invasive cardiac intervention, wherein said plurality ofoptical sensors comprise Fabry-Perot MOMS pressure sensors and saidsensor locations are spaced apart lengthwise along said length of thedistal end portion to provide for one or more of: a) placement of atleast one pressure sensor in the aorta downstream of the aortic valveand placement of at least one pressure sensor in the left ventricle,upstream of the aortic valve for measurement of a transvalvular bloodpressure gradient for the aortic valve; b) placement of at least onepressure sensor in the left atrium upstream of the mitral valve andplacement of at least one pressure sensor in the left ventricle,downstream of the mitral valve for measurement of a transvalvular bloodpressure gradient for the mitral valve; c) placement of at least onepressure sensor in the right atrium upstream of the tricuspid valve andplacement of at least one pressure sensor in the right ventricle,downstream of the tricuspid valve, for measurement of a transvalvularblood pressure gradient for the triscuspid valve; and d) placement of atleast one pressure sensor in the right ventricle upstream of thepulmonary valve and placement of at least one pressure sensor in thepulmonary artery, downstream of the pulmonary valve for measurement of atransvalvular blood pressure gradient for the pulmonary valve.
 21. Theapparatus of claim 20, wherein the sensor arrangement further comprisesa sensor for measuring at least one of temperature and flow.
 22. Theapparatus of claim 20, wherein the sensor arrangement further comprisesan optical thermoconvection sensor.
 23. The apparatus of claim 20 in theform of a steerable guidewire comprising a coil and a core-wire, whereinthe tubular covering layer comprises the coil of the guidewire, thecore-wire extends axially through the coil from the proximal end and thedistal end, and said multi-sensor assembly comprising said plurality ofoptical fibers and optical sensors is assembled around the core-wire.24. The apparatus of claim 23, wherein flexible distal tip enablesintroduction of the distal end portion through a heart valve, andwherein the coil and the core-wire provide the distal end portioncontaining the plurality sensors with flexibility to be introduced intoa chamber of the heart and through the heart valve, together withstiffness to constrain movement of the plurality of sensors in regionsof turbulent flow within the heart.
 25. A control system for controllingthe apparatus of claim 1, wherein the control system comprises a lightsource and detector for coupling, through said optical fibers, to eachof the optical sensors, and optionally comprises electrical connectionsfor an electrical sensor.
 26. The control system of claim 25, whereinthe system further comprises a processor configured for processingoptical data indicative of pressure gradient values and optionally,optical or electrical data indicative of flow velocity values.
 27. Thecontrol system of claim 25, for measuring intravascular or transvalvularblood pressure gradients, and further comprising a processor configuredfor graphically displaying a blood pressure gradient and optionally flowvelocity data, for one or more time intervals, and during one or morecardiac cycles.